Flowering Hedge - Knowledgebase Question

Any suggestions for an annual or perennial flower that would make a good 15"-24" high hedge in full sun? I don't mind planting an annual every year as long as it's fast growing. I live in zone 7 with wet, cool springs, and sandy, slightly acidic soil.

Full sun and sandy soil make your site perfect for lavender, Agapanthus, Shasta daisies, Mexican Sunflowers, Delphinium, Scabiosa or Liatris (Gay Feather). With the exception of the sunflowers, all of these plants are perennial, and all will do well in your maritime Northwest garden.